1. Field of the Invention
The present invention relates to a method for the manufacture of very dense oxidic nuclear fuel bodies of UO.sub.2 with additions of rare earth oxides such as gadolinium oxide. Such nuclear fuel bodies are required particularly for the fuel assemblies of nuclear light-water reactors; the rare-earth oxide, especially Gd.sub.2 O.sub.3, plays the role of a burnable poison.
2. Description of the Prior Art
In sintering directly mixed uranium-gadolinium powders pressed without additions, it has been found that the sintering process deviates from that with pure UO.sub.2 in important ways. In particular, the densities required in the range around 6% by weight can barely be achieved or maintained in spite of very long sintering times. Thorough investigations have shown that in the course of the sintering process, diffusion-stable and therefore sintering-inhibiting phases can form. This manifests itself particularly by the fact that the sintering densification takes place with delay in the temperature range above 1200.degree. C. This effect is pronounced particularly with gadolinium contents around 6% by weight, but extends over the entire range of about 4 to 8% by weight.
Up to now, mainly Gd.sub.2 O.sub.3 concentrations of 2 to 4% have been used in light-water reactors. Since, however, an increase of the concentration is desirable, especially in view of the use in fuel assemblies with high target burnup, the problem arose to find a sintering method with which it is possible to also obtain the higher weight contents of gadolinium oxide without the difficulties mentioned, especially with respect to the sintering density with controlled structure.